1. Field of the Invention
The present invention relates to an anti-spalling edging, in particular, though not exclusively for concrete.
2. Description of the Related Art
Concrete is strong in compression, but weak in tension. Small sections are liable to fail in shear. The result is that edges of concrete slabs are liable to spall, that is the edge is liable to crack away, generally at angle.
The problem can be relieved to an extent by a flat steel edging, with may form part of a joint allowing contraction of the slabs on setting and thermal expansion. Flat steel strip can become bent away from the concrete, thus the original problem is not really solved. The steel strip can be reinforced against such bending away by provision of an in-turned edge or return level with the top of the slab. This protects the edge of the slab, but loading, deflections and impact can allow the free edge of the return to lift. This gives rise to another set of problems. In turn the free edge can be turned down and provided with cut-outs for its anchoring in the slab.
Again there is a problem, in that the down-turn has a radius of curvature at its abutment with the top surface of the concrete, which creates yet another potential spalling site.
In our International Application No WO 2010/094910 (Our '910 Application), we have described and claimed an anti-spalling edging comprising:                a metal strip adapted for concrete to be cast against,        a return along a top edge of the strip,        a down-turn from the edge of the return spaced from the strip,        cut-outs in the down-turn for anchoring it in the concrete;wherein:        the cut-outs are so arranged as to provide faces, extending through the return and generally in the direction of the edging, against which faces the concrete abuts when cast level with the outer surface of the return.        
In our '910 Application, we envisaged that anti-spalling advantage could be obtained if the faces were non-planar, such as being S or W shaped when viewed in plan, preferably the faces are flat and face directly away from a bend connecting the metal strip to the return. We preferred in the direction of the edging, the transverse faces to predominate compared with fingers of the down-turn extending down between the cut-outs.
We envisaged that the fingers might not joined at their distal ends, but we preferred to join them at their distal ends to stabilise them during installation and casting of the concrete. Members joining the fingers are important for holding the finger from drawing upwards of the concrete.
We envisaged that the metal strip would be of steel galvanised before or after is punching of its cut-outs. However, it could also be of stainless steel, mild steel or plastics materials.
In the preferred embodiment of our '910 Application, a pair of anti-spalling edgings were normally to be provided as a “joint” between two sections of concrete slab, the two metal strips abutting with the returns extending in opposite directions on laying of the concrete and separating on curing. The joint would normally include dowels extending into the two sections of the slab, for vertical load transfer in use; the dowels may be any type of dowels and indeed are optional. Furthermore, a single anti-spalling edging might be used, particularly at an edge.
In testing this joint with admittedly-heavy, localised repetitive loading, we have experienced impacting of the return below neighbouring regions of the edge and the concrete not subjected to the localised load.